A battery is configured to charge electric energy and supply the electric energy to various types of electronic devices. In particular, a secondary battery (cell) may recharge electric energy and is implemented by stacking a plurality of cells to increase an output. Accordingly, the secondary battery including the plurality of cells requires a battery management system (hereinafter, referred to as ‘BMS’) configured to manage the plurality of cells. When the plurality of cells are connected in series, the inter-cell balancing is an important factor. The inter-cell balancing may be the cell balancing that maintain each voltage charged in the plurality of cells configuring the battery within an allowable range. The cell balancing correlates with a battery lifespan, output power, and the like and when the cell balancing is not properly made, the cell deteriorates, and as a result, the lifespan and the output power of the battery may be reduced.
As the conventional method of creating the cell balancing, a method of reducing a cell voltage by disposing separate resistors in the plurality of cells, respectively and measuring the voltage of the respective cells to discharge the voltage through the resistors when cell having a substantially high voltage has been developed. In the battery configured of a first cell and a second cell, it is assumed that a voltage of the first cell is greater than that of the second cell. When the first cell and the second cell are simultaneously charged, the first cell is first charged up to a highest voltage within an allowable range. In particular, the first cell performs a discharging operation through the resistor and the second cell terminates a charging operation. Further, when the first cell is discharged up to a predetermined voltage, the first cell and the second cell are simultaneously charged again. When a voltage difference between the first cell and the second cell is within a predetermined range by repeating the operation, the balancing terminates.
However, the battery in which the plurality of cells are connected needs to be provided in the same cell specification to balance deviations such as resistance or voltage among the plurality of cells and has a structure in which the battery management system manages each of the cells.